DISCOVERY OF ATMOSPHERIC MUON NEUTRINO OSCILLATIONS
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1DISCOVERY OF ATMOSPHERIC MUON NEUTRINO OSCILLATIONS
Prologue First Hint in Kamiokande Second Hint in Kamiokande Evidence found in Super-Kamiokande Nov-12 Accident Progress in the K2K Experiment Future
Yoji TotsukaFor
Kamiokandeand
Super-KamiokandeCollaborators
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2Kamiokande Detector(Kamioka Nucleon Decay Experiment)
Search for proton decay3000ton water1000 50cm PMT (20% photo coverage)1000m undergroundMin det. energy ~ 20 MeV (later ~ 7 MeV)1983-1996
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3Atmospheric Neutrinos (1)
The most severe background to proton decay search
100MeV – 1000GeV : e ~ 2 : 1
(low E)p, He
νe
Super-K
μ±
νμ
π±
atmosphere
e±
earth
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4
Interaction in the rock
FC + PC
through-going muons
stopping muons
Initial neutrino energy spectrum
FC
Through-going muons
Stopping muons
Event topology
PC
e + N e + X + N + X + N + X
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5First Hint (2.87kt·yr, 1988)
data MC
events e events e
single ring
178 60(0.34±0
.05)
232.5 110.3(0.47)
-like 85 52 144.0 103.8
e-like 93 8 88.5 6.5
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6/e Identification with a test beam
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7
Earth
Up-down symmetryof the flux
Atmospheric Neutrinos (2)
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8Second Hint (7.7kt·yr, 1994)
sub-GeV data MC
events e events e
single ring 482 182 584.3 270.5
-like 234 158 356.8 247.9
e-like 248 24 227.6 22.6
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9
40m
41.4m
Super-Kamiokande (1996)1996-50000ton water11146 50cm PMT (40% photo coverage)1000m undergroundMin det. energy ~ 5 MeV
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10Evidence for Oscillation of Atmospheric Neutrinos(33.0kt·yr, 1998)
sub-GeV data MC (+-20%)
single ring 2389 2622.6
-like 1158 1573.6
e-like 1231 1049.1
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11Upward-going muons
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12
2=170.8/170 d.o.f. at (sin2223, m232)=(1.00, 2.0x10-3eV2)
2=445.2/172 d.o.f. (null oscillation)
1489 day FC+PC data + 1646 day upward going muon data
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13Allowed region of the oscillation parameters
Assuming oscillation
Best fit 2
min = 170.8/170 d.o.fat (sin2223 m23
2) = (1.0, 2.0 x 10-3 eV2)
90% CL allowed regionsin2223> 0.91.3x10-3 < m23
2 <3.0x10-3 (eV2)
Assuming null oscillation 2 = 445.2/172 d.o.f
(complete SK-I dataset)
Soudan-2
MACRO
Super-K68% CL90% CL99% CL
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14Nov-12 Accident
6777 ID + 1100 OD PMTs destroyed
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15
Partial rebuilding 5248 ID PMTs
(47% of pre-accident density) 1885 OD PMTs Ready by end 2002
Full rebuilding Additional 5898 new ID PMTs Ready by April 2007
As of April 1
Resurrection
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16Next steps
Tau appearance
+ N - + X
Oscillation patternDip in L/E distribution
P( ) = 1 - cos4sin22 sin2(1.27m232L/E)
- P( e) P(e) = sin22 sin2 sin2(1.27m13
2L/E)
70 yr Monte Carlom2=2.5×10-3eV2
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17K2K long baseline neutrino oscillation experiment
5.6×1019 pot (June 1999 – July 2001)
250 km
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18
Best fit 1R spectrum & Nsk
Best fit point (sin2223 , m232) =
(1.0, 2.8x10-3eV2) KS test prob.(shape): 79% NSK=54 (Obs.=56) Very good agreement in shape & NSK wit
h atmospheric neutrinos
Expected w/o oscillationNormalized w/o oscillationNormalized with best fit oscillation
Total number of obs. Events: 56 16 (Jan03-Apr03)
Expected w/o oscillation: 80.6 +7.3-8.0 24 +2.3-2.1
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19T2K (Tokai-to-Kamioka)
J-PARCHyper-Kamiokande
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20
JHF MINOS K2K
E(GeV) 50 120 12
Int.(1012ppp) 330 40 6
Rate(Hz) 0.29 0.53 0.45
Power(MW)
Phase-II
0.77
4
0.41 0.0052
50 GeV JHF PS 2007
Kamioka
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21Expected sensitivities (5yrs)
0.01
1×10-4
True m232 (eV2)
(sin22) ~ 0.01 (m2) ~ <1×10-4
OAB-2degree
disappearance
w/ beam MC, & full SK det. simulation
(si
n2 2
)(
m23
2 )
excludedby reactor
132
2322 2sinsin2sin e
~0.5sin2213>0.006 (90%)sin2213>0.018 (3)
x20
Sensitivityin 5 years
NBB 1.5GeV
NBB 3 GeV
e appearance
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22Hyper-Kamiokande (1Mt water)
Precision neutrino oscillation study Proton decay search
R&D (complete in 2 years) Cavity excavation and its stability New light detector: Hybrid Photo-
Detector, HPD (50cm)
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23
Thank you
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24Oscillation Among 3 Flavors
P(e) = sin22 sin2 sin2(1.27m132L/E)
P( ) = 1 - cos4sin22 sin2(1.27m232L/E) - P( e)
sin213 < 0.1, cos413~1 (from the CHOOZ experiment)
sin22 ~ sin2223 ~ 1,sin22e = sin2213 sin223 ~ 0.5 sin2213 ~ 2|Ue3|2
m3
m2
m1
m3 >> m2 > m1